HIFU projects:? The studies being carried out using high intensity focused ultrasound (HIFU) involve a unique variety of novel applications for drug delivery and other therapies. The basis of these applications is !: an in-depth understanding of the ultrasound mechanisms for producing bio-effects in the tissues, both destructive and non-destructive 1, as well as 2. the pre-clinical safety and bridging studies required to bring drug plus device paradigms to clinical practice in patients, and 3. the optimization of techniques and technologies for uterine fibroid image guided ablation. The following is a description of the different studies that are presently on going:? ? I - Enhanced local drug deposition using low temperature sensitive liposomes (LTSLs)? In studies carried out in mice, we have previously shown that we can enhance local doxorubicin delivery in both tumors 2 and muscle 3 by combining systemic injections of LTSLs containing the drug and pulsed-HIFU exposures. In the tumor studies, enhanced delivery was compared to non-thermo sensitive liposomes and shown to produce improved anti-tumor effects. These exposures typically generate temperature elevations that are just a few degrees Celsius above body temperature, which are non-destructive, and which cause a phase transition in the liposomes making them more permeable and able to release their payload. Presently, we are using a multi-disciplinary approach to optimize these treatments for improving spatial and temporal heating using computer simulations, in vitro experimentation, and in vivo studies. Results are then being translated to larger animal models using an MR-guided HIFU system. Recently, we have also started evaluating the potential of combining LTSLs with HIFU induced thermal ablation for increasing the volume of ablated tissue.? ? II - Enhanced local drug deposition through non-destructive and destructive mechanisms.? In comparison to work with the LTSLs, pulsed-HIFU exposures can also generate mechanical (i.e. non-thermal) effects in tissue which transiently enhance tissue permeability therefore improving the delivery of various agents possessing different formulations. This includes plasmid DNA 4, monoclonal antibodies 5 and small molecule chemotherapeutic agents 6. In the case of the latter, we were able to show improved growth inhibition in murine tumors when using the proteasome inhibitor, bortezomib. We are presently evaluating new agents for this purpose including those for gene delivery applications 7. At the same time, we are carrying out mechanistic investigations to characterize the manner by which these delivery enhancing effects occur; this will assist in optimization of the exposures. To date, we have provided preliminary evidence for a novel ultrasound mechanism for enhancing drug delivery based on acoustic radiation force induced displacements 1,8,9. Thermal ablation will also deposit heat that can add to enhanced permeability and retention as well as mechanical deployment of heat-sensitive nanoparticles.? ? III - Induced effects for enhancing immunotherapy of tumors? Various studies have shown that HIFU ablation can enhance adaptive immunity against tumors. It is hypothesized that in addition to destroying tumor tissue, tumor associated antigens (TAA) are being released that can stimulate the immune system to create these effects. We are presently investigating the potential of combining various types of exposures, where each one would have a specific effect, including pre-treating to boost levels of TAAs, as well as modified exposures for increasing their release. Evaluations are being carried out using standard immune assays and tumor challenge models.? ? IV - Enhanced tPA mediated thrombolysis? The versatility of pulsed-HIFU exposures for enhancing drug delivery is seen in studies on thrombolysis. We have shown that pre-treating whole blood clots with pulsed-HIFU can increase binding and penetration of tissue plasminogen activator (tPA) into the clots, and consequently improve rates of thrombolysis in vitro 10 and in vivo 11. The latter study was carried out in a novel thrombolysis model that we developed in the marginal ear vein of rabbits. We are presently developing an in vivo model for deep vein thrombosis (DVT) to evaluate the potential of our exposures to treat these more advanced clots.? ? V - Safety: Studies on the potential of HIFU exposures for enhancing metastasis? HIFU exposures can produce a variety of effects for both adjunct and stand alone treatments of tumors. In the case of non-destructive exposures, where the aim is to enhance the permeability of the tissues, there exists the potential that these exposures may also be enhancing metastasis by aiding the process of cell detachment and infiltration into the host tissue. We are presently characterizing a number of highly metastatic murine cell lines, where the aim is to be able to quantitatively determine the potential of various types of HIFU exposures for enhancing metastasis. These studies are being carried out using standard procedures such as counting metastasis in the lungs, as well as tracking metastatic lesions using stably transfected cell lines expressing reporter genes for in vivo imaging. ? ? VI - FIbroid Ablation:? Plans are underway to begin human trials for the use of MRI-guided """"""""Spiral HIFU"""""""" for the treatment of uterine fibroids and to compare the technique to uterine artery embolization (both are minimally invasive alternatives to more costly and invasive surgery like hysterectomy).
